In a fuel tank of a motor vehicle, fuel vapors are generated which basically can escape through a deaeration and/or aeration path into the environment of the vehicle. Such a path connected to the environment is required, e.g., for a pressure compensation. To reduce or avoid such pollutant emissions as far as possible, deaeration and aeration systems are used which comprise a filter device. Such a filter device which, for example, works with activated carbon, can extract hydrocarbons from a gas flow by means of sorption, thus by means of adsorption and/or absorption. By backwashing the filter device, for example with ambient air, embedded hydrocarbons can be removed by means of desorption in order to regenerate the filter device or its storage material.
In vehicle applications, in particular, the following states are differentiated from each other:
Refueling process or ORVR (Onboard Refueling Vapor Recovery). During refueling the stationary vehicle with the internal combustion engine turned off, an air-fuel vapor mixture is displaced by the fuel flowing into the tank, among other things, in the direction of the environment. In order that statutory emission limit values are not exceeded here, the deaeration and aeration system adsorbs the pollutants contained in the gas that flows out.
Vehicle standstill or DBL (Diurnal Bleeding Loading). With the vehicle stationary and the internal combustion engine turned off, diffusion processes and thermal expansion effects result in the spread of hydrocarbon-containing gases from the vehicle tank toward the environment. In order that here, too, the statutory emission limit values are not exceeded, the deaeration and aeration system adsorbs the pollutants contained in the gas that flows out.
Washing. With the internal combustion engine turned on, thus in particular during a driving operation of the vehicle, air from the environment is sucked in by the deaeration and aeration system, whereby the adsorbed pollutants are desorbed and thus the deaeration and aeration system is regenerated.
To be able to prevent or reduce the pollutant emission in different states over a sufficiently long period of time, there is the possibility to equip the respective filter device with a comparatively large storage volume for a suitable sorption material which, in particular, can be distributed over a plurality of chambers through which a flow can pass in succession. In order that the storage material does not have an inadmissibly high flow resistance it has to be structured once a certain amount or a certain volume is reached, which involves a significant effort.
From U.S. Pat. No. 6,540,815 B1, a deaeration and aeration system is known by means of which the emission values for a fuel tank of a motor vehicle with internal combustion engine can be reduced. For this purpose, the deaeration and aeration system is equipped with a main filter device which has an outlet and an inlet that is fluidically connectable to the fuel tank, and is equipped with an additional filter device which has an inlet that is fluidically connected to the outlet of the main filter device and an outlet that is fluidically connectable to the environment of the vehicle. The known deaeration and aeration system is operated in such a manner that during a standstill of the vehicle with the internal combustion engine turned off, gas escaping from the tank is conveyed through a main filter device and subsequently through an additional filter device and into the environment, and that during a driving operation of the vehicle with the internal combustion engine turned on, air from the environment is sucked in through the additional filter device and subsequently through the main filter device.